An example of electronic advertisement bulletin boards provided on buildings or the like utilizes a (multi-display or multi-monitor) technique in which a plurality of display panels (i.e., displays) are arrayed in one or both of the vertical and horizontal directions so as to display one image (as a whole) on the whole of the displays and thus implement a large screen.
In an image display system utilizing the above multi-display technique, the whole of the individual display panels display one image. Therefore, when each display panel employs an ordinary display device, a display shift of one frame may be produced between upper and lower (adjacent) display panels. More specifically, each display panel displays an image by scanning each frame in the horizontal direction while simultaneously scanning the frame in the vertical direction. For example, it is assumed that each display panel has n lines (horizontal lines). In this case, the display panel performs the relevant drawing process from the first line (the top of the display panel) to the last n-th line (the bottom of the display panel) to complete the display of the target image. In order to display a video, based on image information items input at every moment, the display panel repeats the above scanning process in the horizontal and vertical directions, for each of different images.
FIG. 6A is a diagram utilized to explain a display shift produced in an image display system related to an embodiment of the present invention. FIG. 6B is a diagram utilized to show an example of displayed images in individual frames.
In FIG. 6A, time is shown along the horizontal axis and the vertical axis corresponds to the vertical direction of each display panel, by which transition in the display image in each display panel is shown. FIG. 6B shows display images of (N−1)th, N-th, and (N+1)th frames.
In the following case, in an image display system utilizing a multi-display in which display panels are arrayed in one or both of the vertical and horizontal directions, the scanning in the vertical direction is synchronously performed between all display panels. In this case, at the moment next to the completion (at time T1) of the drawing of the n-th line where the (N−1)th image is displayed on the entire screen, the individual display panels simultaneously start the drawing of the first line of a different image (i.e., image N) (see FIG. 6A). Then, of any two vertically adjacent display panels, the upper display panel still displays the n-th line of the (N−1)th image while the first line of the lower display panel already displays the N-th image. In the image display system using a multi-display, ideally, all display panels display the same image. However, in the above-described display device, a display shift of one frame is always produced at the boundary between the upper and lower adjacent display panels.
Patent Document 1 displays a technique in which of any two vertically adjacent display panels, the start time of the vertical scanning of the lower display panel is delayed by one frame. According to this technique, it is possible to cancel a display shift of one frame produced at the boundary between the upper and lower adjacent display panels.